Piezoelectric element, liquid droplet ejection head, actuator, and vibrator

Abstract

A piezoelectric element, a liquid droplet ejecting head, an actuator, and a vibrator that can improve electrical characteristics are provided. A piezoelectric element (44) includes a first electrode (441) formed on a substrate (36), a seed layer (442) formed on the first electrode (441), a piezoelectric film (443) formed on the seed layer (442) and containing potassium, sodium, and niobium, and a second electrode (444) formed on the piezoelectric film (443), the piezoelectric film (443) containing lithium and one or more first transition elements, the seed layer (442) containing bismuth, when the piezoelectric film (443) is bisected in a stacking direction and the second electrode (444) side is set as a first region (443f) and the first electrode (441) side is set as a second region (443s), a bismuth intensity at a boundary (s2) between the first region (443f) and the second region (443s) obtained by secondary ion mass spectrometry is one-fifth or less of a maximum bismuth intensity of the piezoelectric film (443) obtained by secondary ion mass spectrometry.

Description

Technical Field

[0001] This invention relates to a piezoelectric element, a droplet ejector, an actuator, and an oscillator. Background Technology

[0002] The development of piezoelectric elements using non-lead piezoelectric materials instead of lead-based piezoelectric materials such as lead zirconate titanate has been ongoing. For example, Patent Document 1 discloses a piezoelectric element using a non-lead piezoelectric material containing bismuth, iron, barium, and titanium. This piezoelectric element comprises a composite oxide layer of the aforementioned non-lead piezoelectric material and a buffer layer containing at least one of bismuth, iron, zinc, and nickel. The buffer layer, also known as a seed layer, is designed to ensure consistent crystal orientation of the composite oxide layer.

[0003] However, in the piezoelectric element described in Patent Document 1, there is a problem that improving the electrical properties is difficult when potassium sodium niobate is used in the piezoelectric material. Specifically, potassium sodium niobate is one of the more promising lead-free piezoelectric materials. When the aforementioned buffer layer is used in the composite oxide layer of potassium sodium niobate, elements contained in the buffer layer easily diffuse into the composite oxide layer due to the heat treatment during manufacturing. When elements in the buffer layer diffuse, the crystal orientation of the composite oxide layer becomes more easily disturbed, resulting in a decrease in the electrical properties of the piezoelectric element. Therefore, in piezoelectric elements using potassium sodium niobate, there is a need to improve the electrical properties.

[0004] Patent Document 1: Japanese Patent Application Publication No. 2013-201407 Summary of the Invention

[0005] The piezoelectric element comprises: a first electrode formed on a substrate; a seed layer formed on the first electrode; a piezoelectric film formed on the seed layer, containing potassium, sodium, and niobium; a second electrode formed on the piezoelectric film, the piezoelectric film containing lithium and one or more first transition elements, the seed layer containing bismuth, wherein when the piezoelectric film is bisected in the stacking direction, and the second electrode side is designated as the first region and the first electrode side as the second region, the bismuth intensity at the boundary between the first region and the second region, as measured by secondary ion mass spectrometry, is less than one-five-hundredth of the maximum bismuth intensity of the piezoelectric film as measured by secondary ion mass spectrometry.

[0006] The droplet ejector head includes the piezoelectric element and substrate described above, and has: a nozzle plate having a nozzle for ejecting droplets; a pressure chamber substrate having a pressure chamber communicating with the nozzle, the substrate forming part of the wall of the pressure chamber, and the piezoelectric element being formed on the substrate.

[0007] The actuator includes the piezoelectric element described above, and further includes: a driving unit that is driven by the piezoelectric element; and a voltage applying unit that applies a voltage to the piezoelectric element.

[0008] The oscillator has the piezoelectric element described above and a charge detection unit that detects the amount of charge generated by the displacement of the piezoelectric element and outputs a signal corresponding to the amount of charge. Attached Figure Description

[0009] Figure 1 This is a schematic diagram showing the general structure of a recording device including the droplet ejection head according to the first embodiment.

[0010] Figure 2 This is an exploded 3D view of the droplet ejector.

[0011] Figure 3 For including Figure 2 The line segment AA in the diagram, and the cross-sectional view along the XZ plane.

[0012] Figure 4 This is a plan view showing the structure of a piezoelectric element.

[0013] Figure 5 For including Figure 4 The line segment EE in the diagram, and the cross-sectional view along the YZ plane.

[0014] Figure 6 A graph showing the depth direction curve of Example 1, achieved by SIMS measurement.

[0015] Figure 7 A graph showing the depth direction curve of Comparative Example 1, achieved by SIMS measurement.

[0016] Figure 8 A graph showing the historical relationship between the applied electric field and polarization in Example 1 and Comparative Example 1. Detailed Implementation

[0017] 1. First Implementation Method

[0018] In the embodiments described below, piezoelectric elements using non-lead piezoelectric materials, droplet ejectors equipped with such piezoelectric elements, and recording devices are illustrated, and their descriptions are based on the accompanying drawings. In the following drawings, the XYZ axes, serving as coordinate axes, are labeled as needed, with the direction indicated by the arrow marked as the "+" direction and the opposite direction as the "-" direction. Sometimes the +Z direction is set upwards and the -Z direction downwards; sometimes, the view from the +Z direction is referred to as a top-down view or a bird's-eye view. Furthermore, for ease of illustration, the sizes of the various components differ from their actual dimensions.

[0019] 1.1. Recording device

[0020] like Figure 1 As shown, the recording device 100 of the inkjet printer has a droplet ejector head 1 according to this embodiment. The droplet ejector head 1 includes a piezoelectric element 44 according to this embodiment, which will be described later.

[0021] In the recording apparatus 100, printing is performed by causing ink droplets to adhere from the droplet ejection head 1 onto the recording medium 2. In addition to the droplet ejection head 1, the recording apparatus 100 also includes a head movement mechanism 5, a media transport mechanism 6, an ink collection unit 7, and a control unit 18.

[0022] The head movement mechanism 5 includes a carriage 4 and a timing belt 8. A droplet ejector head 1 is mounted on the carriage 4. The carriage 4 and the timing belt 8 are connected together. The timing belt 8, driven by a motor (not shown), moves the carriage 4 in the X-axis direction, which is the main scanning direction. Thus, the droplet ejector head 1 can reciprocate relative to the recording medium 2 in the X-axis direction.

[0023] The media delivery mechanism 6 delivers the recording medium 2 in the +Y direction, which is the sub-scanning direction. As a result, the recording medium 2 moves relative to the droplet ejection head 1 in the +Y direction.

[0024] The ink collection unit 7 collects the ink ejected from the droplet ejector head 1. The ink collected in the ink collection unit 7 is supplied to the droplet ejector head 1 via an ink piping (not shown). Multiple ink collection units 7 may be configured to correspond to various types of inks, such as black, blue-green, magenta, and yellow. Furthermore, the droplets ejected from the droplet ejector head 1 are not limited to ink; they may also be droplets other than ink, such as processing fluids or cleaning fluids.

[0025] The droplet ejector head 1 is positioned on the carriage 4 on the side opposite to the recording medium 2. The droplet ejector head 1 has a nozzle surface (not shown) on the surface opposite to the recording medium 2. Multiple nozzles N are provided on the nozzle surface. The multiple nozzles N are arranged in a manner corresponding to the types of inks described above.

[0026] The ink in the ink collection section 7 is supplied to the droplet ejection head 1, and is ejected as droplets from multiple nozzles N by the actuator of the droplet ejection head 1 (described later). The ejected ink droplets fall and adhere to the recording medium 2.

[0027] The control unit 18 includes multiple processing circuits such as CPUs (Central Processing Units) or FPGAs (Field Programmable Gate Arrays), and storage circuits such as semiconductor memories. The control unit 18 controls the overall operation of the recording device 100. The head moving mechanism 5, the media conveying mechanism 6, and the droplet ejection head 1 are electrically connected to the control unit 18 and are comprehensively controlled by the control unit 18.

[0028] As described above, by moving the droplet ejector head 1 in the main scanning direction in accordance with the transport of the recording medium 2 in the sub-scanning direction, and by attaching ink to the recording medium 2 at a predetermined time, an image or the like is printed on the recording medium 2.

[0029] Although a serial printer is exemplified as a recording device 100 in this embodiment, the recording device suitable for the droplet ejector head 1 is not limited to this. For example, the droplet ejector head of the present invention may also be a line printhead, and the recording device may also be a line printhead printer. Furthermore, the device that mounts the droplet ejector head of the present invention is not limited to the recording device 100, and may also be, for example, a manufacturing apparatus for color filters such as liquid crystal displays, an electrode forming apparatus such as organic electroluminescent displays or field emission displays, a biochip manufacturing apparatus, etc.

[0030] 1.2. Droplet ejector

[0031] like Figure 2 As shown, the droplet ejector head 1 includes a nozzle plate 62, two vibration absorbers 64, a flow channel forming substrate 32, a pressure chamber substrate 34, a piezoelectric element 44, a vibrating plate 36 serving as a substrate, a wiring substrate 46, a drive circuit 50, and a frame portion 48. The nozzle plate 62, vibration absorbers 64, flow channel forming substrate 32, pressure chamber substrate 34, vibrating plate 36, and wiring substrate 46 are generally rectangular plate-shaped components, and their long sides are along the Y-axis when viewed from above.

[0032] In manufacturing the droplet ejector head 1, the nozzle plate 62, two vibration absorbers 64, flow channel forming substrate 32, pressure chamber substrate 34, vibrating plate 36, wiring substrate 46, and frame portion 48 are stacked in this order and bonded together with each other, for example, by an adhesive.

[0033] The nozzle plate 62, the flow channel forming substrate 32, the pressure chamber substrate 34, and the vibrating plate 36 have a structure that is substantially linearly symmetrical about their respective centerlines along the X-axis. Viewed from above, the pressure chamber substrate 34, the vibrating plate 36, and the wiring substrate 46 are smaller in size compared to the flow channel forming substrate 32 and the frame portion 48.

[0034] Multiple nozzles N are formed on the nozzle plate 62. Each nozzle N is a through hole formed by perforating the nozzle plate 62, and is approximately circular when viewed from above. The multiple nozzles N are arranged along the Y-axis and in two rows along the X-axis. Two vibration absorbers 64 are arranged in a manner that clamps the nozzle plate 62 along the X-axis. The two vibration absorbers 64 are flexible thin films.

[0035] The flow channel forming substrate 32 has two first openings 32a, a plurality of second openings 32b, and a plurality of third openings 32c. The first openings 32a are generally rectangular in shape with their long sides along the Y-axis when viewed from above. The first openings 32a are provided along the long side of the flow channel forming substrate 32 along the Y-axis when viewed from above.

[0036] Multiple second openings 32b are arranged in two columns along the Y-axis. Similarly, multiple third openings 32c are also arranged in two columns along the Y-axis. Along the X-axis, a column of one first opening 32a, a column of one second opening 32b, a column of one third opening 32c, a column of one second opening 32b, and a column of the other first opening 32a are arranged in this order. Furthermore, adjacent second openings 32b and third openings 32c along the X-axis are arranged in a manner where their positions are approximately identical along the Y-axis.

[0037] A plurality of openings 34a are provided on the pressure chamber substrate 34. Each opening 34a is approximately rectangular in shape with its long side along the X-axis when viewed from above. The plurality of openings 34a are arranged in two rows along the Y-axis. The two rows of openings 34a are arranged in a manner that allows them to be aligned along the X-axis. Each opening 34a is located at a position that overlaps with the second opening 32b and the third opening 32c adjacent to the flow channel forming substrate 32 when viewed from above.

[0038] Piezoelectric elements 44 are formed on the vibrating plate 36. Specifically, a plurality of piezoelectric elements 44 are arranged on the main plane above the vibrating plate 36. Each of the plurality of piezoelectric elements 44 is disposed at a position that overlaps with a plurality of openings 34a of the pressure chamber substrate 34 when viewed from above. Each opening 34a of the pressure chamber substrate 34, together with the lower surface of the vibrating plate 36, forms the pressure chamber C, which will be described later.

[0039] The drive circuit 50 drives the piezoelectric element 44. Specifically, the drive circuit 50 is an IC (Integrated Circuit) chip that outputs a drive signal for driving the piezoelectric element 44 and a reference voltage. The drive circuit 50 is mounted on the main plane above the wiring substrate 46. On the wiring substrate 46, wiring is provided for the input signal to the drive circuit 50, the drive signal output from the drive circuit 50, and the reference voltage.

[0040] Terminals (not shown) of the wiring board 46 and the piezoelectric element 44 are joined together via bumps B, described later. The terminals described above receive input signals to the directed drive circuit 50, for example, via an FPC (Flexible Printed Circuit).

[0041] The frame portion 48 is a container for storing ink and is frame-shaped. When the droplet ejector head 1 is assembled, a pressure chamber substrate 34, a vibrating plate 36, and a wiring substrate 46 are disposed in the internal space of the frame portion 48. Through holes 48a are formed on both sides of the frame portion 48 along the X-axis direction.

[0042] like Figure 3 As shown, a wiring substrate 46, a vibrating plate 36, and a pressure chamber substrate 34 are housed inside the frame-shaped frame portion 48. The outer edge of the frame-shaped frame portion 48 is connected to the top of the flow channel forming substrate 32. A nozzle plate 62 and two vibration absorbers 64 are connected to the bottom of the flow channel forming substrate 32. Here, the droplet ejection head 1 has Figure 3 The structure is symmetrical about the left and right sides of the Earth. Therefore, in the following description, we will focus on the structure on the left side, i.e., the -X direction, and omit the description of the structure in the +X direction.

[0043] A space Rb is formed near the end of the frame portion 48 in the -X direction. The upper part of the space Rb communicates with the through hole 48a, and the lower part communicates with the first opening 32a of the flow channel forming substrate 32. The space Rb extends in the Y-axis direction in a manner corresponding to the top view shape of the first opening 32a.

[0044] A space Ra, a partition wall 32d, a supply channel 26b, and a connecting channel 26c are provided on the flow channel forming substrate 32. The space Ra is an internal space formed by the first opening 32a. The partition wall 32d is disposed between the first opening 32a and the second opening 32b. The lower end of the partition wall 32d is recessed in the +Z direction, positioned above the lower surface of the flow channel forming substrate 32. A supply liquid chamber 26a is formed through the lower end of the partition wall 32d and the upper surface of the vibration absorber 64. The supply channel 26b is an internal space formed by the second opening 32b.

[0045] A pressure chamber C is formed through the opening 34a of the pressure chamber substrate 34, the surface below the vibrating plate 36, and the surface above the flow channel forming substrate 32. That is, the vibrating plate 36 forms part of the upper wall of the pressure chamber C. The pressure chamber C communicates with the supply flow channel 26b at the lower end in the -X direction.

[0046] The connecting flow channel 26c is an internal space formed by the third opening 32c. The pressure chamber C is connected to the connecting flow channel 26c at the lower end in the +X direction, and is connected to the nozzle N of the nozzle plate 62 via the connecting flow channel 26c.

[0047] As described above, the through hole 48a, spaces Rb and Ra, supply liquid chamber 26a, supply flow channel 26b, pressure chamber C, connecting flow channel 26c, and nozzle N are connected in the above order to form an ink flow channel. In the structure that forms the ink flow channel, the supply liquid chamber 26a and the connecting flow channel 26c are arranged in such a way that they correspond to the plurality of nozzles N respectively.

[0048] Ink is supplied from the ink receiving section 7 through the through hole 48a. Spaces Ra and Rb function as liquid storage chambers for storing the ink supplied to the pressure chamber C. Space Rb is connected to a plurality of spaces Ra arranged along the Y-axis. The ink supplied from the through hole 48a is stored in space Ra via space Rb. The ink stored in space Ra is supplied to the pressure chamber C via supply liquid chamber 26a and supply flow channel 26b.

[0049] The piezoelectric element 44 is arranged to overlap with the pressure chamber C in a top view. That is, multiple piezoelectric elements 44 are arranged in a manner corresponding to multiple pressure chambers C. The piezoelectric element 44 includes an active part 440, which will be described later. A wiring board 46 is disposed above the piezoelectric element 44, and a drive circuit 50 is disposed above the wiring board 46. The wiring board 46 and the piezoelectric element 44 are electrically connected via a bump B.

[0050] A drive signal and a reference voltage are input to the piezoelectric element 44 via the bump B from the wiring board 46. The piezoelectric element 44 deforms due to the applied voltage from the drive signal and the reference voltage. The vibrating plate 36 vibrates in conjunction with the deformation of the piezoelectric element 44. In this way, the ink is ejected from the nozzle N by the pressure change within the pressure chamber C.

[0051] The vibrating plate 36 is driven by the piezoelectric element 44. The aforementioned drive circuit 50 applies a voltage to the piezoelectric element 44. Here, the piezoelectric element 44, the vibrating plate 36 which also serves as the drive unit, and the drive circuit 50 which serves as the voltage application unit constitute the actuator 101 of this embodiment. Although details will be described later, since the piezoelectric element 44 improves electrical characteristics, an actuator 101 with superior electrical characteristics can be provided. Furthermore, the actuator equipped with the piezoelectric element of the present invention is not limited to the structure described above.

[0052] 1.3. Piezoelectric elements

[0053] like Figure 4 As shown, the piezoelectric element 44 according to this embodiment includes a first electrode 441, a seed layer 442, a piezoelectric film 443, and a second electrode 444, which are formed on a vibrating plate 36 (not shown) as a substrate. Although details will be described later, the elements are stacked in the order of first electrode 441, seed layer 442, piezoelectric film 443, and second electrode 444, starting from the vibrating plate 36 and moving upwards along the Z-axis. Furthermore, in relation to… Figure 4 Unless otherwise specified, the following descriptions are intended to depict the view from above.

[0054] The first electrodes 441 are respectively arranged overlappingly in the direction along the Z-axis relative to the pressure chamber C. The first electrodes 441 extend in such a way that they are pulled out in the +X direction from a generally rectangular region overlapping with the pressure chamber C. Although not shown in the figure, the plurality of first electrodes 441 are individually electrically connected to the aforementioned drive circuit 50 at their extension points in the +X direction.

[0055] In the manufacturing process of the piezoelectric element 44, after the seed layer 442 and the piezoelectric film 443 cover the plurality of first electrodes 441 and are formed into a substantially dense state, only region 443a is etched. That is, in region 443a, the seed layer 442 and the piezoelectric film 443 are not disposed. Region 443a is a relatively elongated, approximately hexagonal shape along the X-axis and is disposed between adjacent first electrodes 441 along the Y-axis.

[0056] The second electrode 444 covers the first electrode 441, the seed layer 442, the piezoelectric film 443, and the region 443a and is formed as a whole surface. A separate voltage is applied to the first electrode 441, while a common voltage is applied to the second electrode 444.

[0057] like Figure 5 As shown, the piezoelectric element 44 is formed by stacking the vibrating plate 36, the first electrode 441, the seed layer 442, the piezoelectric film 443, and the second electrode 444 in the order described above, facing upwards. Here, the area where the first electrode 441, the seed layer 442, the piezoelectric film 443, and the second electrode 444 overlap in a top view is designated as the active part 440.

[0058] The active portion 440 is the region where the piezoelectric film 443 deforms when a voltage is applied between the first electrode 441 and the second electrode 444. The active portion 440 is positioned opposite the pressure chamber C via the vibrating plate 36 in the direction along the Z-axis.

[0059] The vibrating plate 36 has a silicon (Si) substrate 361 and an insulating layer 362. The silicon substrate 361 is made of monocrystalline silicon. Alternatively, an SOI (Silicon on Insulator) substrate or a glass substrate may be used instead of the silicon substrate 361.

[0060] The insulating layer 362 is made of zirconium oxide (ZrO2). Although not shown in the figure, a layer of silicon oxide (SiO2) is provided on the surface above the insulating layer 362 in the silicon substrate 361.

[0061] A first electrode 441 is formed on the vibrating plate 36. That is, the first electrode 441 is disposed in contact with the surface above the insulating layer 362 of the vibrating plate 36. Although not shown in the figure, the first electrode 441 is composed of a platinum (Pt) layer and an iridium (Ir) layer. However, the first electrode 441 is not limited to being composed of a platinum layer and an iridium layer. The first electrode 441 may also be a single layer of a metal material such as titanium (Ti), platinum, iridium, aluminum (Al), nickel (Ni), gold (Au), or copper (Cu), or it may be a structure composed of two or more single layers of the above-mentioned metal materials stacked together.

[0062] The thickness Tu of the first electrode 441 is preferably 20 nm or more and 300 nm or less.

[0063] The seed layer 442 controls the crystallization orientation of the composite oxide in the piezoelectric film 443 in a manner that ensures uniformity. The seed layer 442 promotes a preferred orientation of the crystallization of the piezoelectric film 443 toward the (100) plane. The seed layer 442 is formed on the first electrode 441 and covers the top and sides of the first electrode 441. The seed layer 442 is preferably a composite oxide containing bismuth (Bi), titanium, iron (Fe), and lead (Pb) and having a perovskite structure.

[0064] Specifically, preferably, the seed layer 442 is composed of Pb x Bi (a-x) Fe y Ti (b-y) O z Let x be a composite oxide, where a > x and b > y. Preferably, x / (ax) satisfies equation (1) below. By including these elements in the seed layer 442, the orientation of the composite oxide crystallization in the piezoelectric film 443 is promoted. As a result, the electrical characteristics of the piezoelectric element 44 can be further improved.

[0065] 0.04 < x / (ax) < 1.40…(1)

[0066] In order to make the composite oxide orientation (100) plane of the piezoelectric film 443 more preferably, x / (ax) satisfies the following formula (2).

[0067] x / (ax)<0.72…(2)

[0068] Furthermore, b = 1 is preferred, a / b satisfies the following equation (3), and z satisfies the following equation (4).

[0069] 0.8 < (a / b) < 1.4…(3)

[0070] 2.8 < z < 3.2…(4)

[0071] Although the composition of the seed layer 442 is not specifically limited, for example, lead is set to 0.1, bismuth to 1.1, iron to 0.5, titanium to 0.5, and oxygen (O) to 3.0 in the molar ratio of each element. Their composition is adjusted, for example, by the molar ratio of each element in the precursor solution of the seed layer 442 during its fabrication. Because the seed layer 442 has a relatively high dielectric constant, the displacement efficiency, as indicated by the displacement of the piezoelectric film 443 relative to the applied voltage, is relatively good.

[0072] A persistent issue in piezoelectric buffer layers is that elements constituting the buffer layer readily diffuse into the piezoelectric composite oxide due to heat treatment and other processes during manufacturing. When diffusion introduces elements of varying valences into the composite oxide, it leads to a high concentration of defects in the piezoelectric crystal. This hinders domain wall movement, resulting in displacement or reduced polarization, ultimately degrading the piezoelectric's electrical properties. Particularly with potassium sodium niobate composite oxides, significant bismuth diffusion tends to exacerbate these adverse effects.

[0073] In contrast, in the piezoelectric element 44, since lithium (Li) is contained in the potassium sodium niobate ((K,Na)NbO3) of the piezoelectric film 443, the occurrence of the aforementioned adverse conditions can be suppressed. The manufacturing method of the piezoelectric element 44 and the structure of the piezoelectric film 443 will be described later.

[0074] The thickness Ts of the seed layer 442 is thinner than the thickness Tu of the first electrode 441. Even with a relatively thin thickness, the seed layer 442, which contains bismuth, titanium, iron, and lead, ensures consistent orientation of the piezoelectric film 443. Therefore, by making the thickness Ts of the seed layer 442 thinner than the thickness Tu of the first electrode 441, the diffusion of bismuth into the piezoelectric film 443 can be further suppressed. The thickness Ts of the seed layer 442 is preferably 5 nm or more and 200 nm or less, more preferably 5 nm or more and 100 nm or less.

[0075] Furthermore, the seed layer 442 is not limited to a perovskite structure. The seed layer 442 can also be an octahedral crystalline structure obtained by coordinating six oxygen atoms in iron or titanium, similar to a perovskite structure. Examples of such crystalline structures include bismuth layered structures. Additionally, the seed layer 442 may contain composite oxides that do not contain one or more of bismuth, titanium, iron, and lead. Moreover, the seed layer 442 may contain composite oxides obtained by partially replacing any one of bismuth, titanium, iron, and lead, provided that the crystal orientation is not disrupted.

[0076] The piezoelectric film 443 is the main part of the piezoelectric element 44, which is deformed by the application of voltage. The piezoelectric film 443 is formed in contact with the top of the seed layer 442 and covers the top of the seed layer 442. The piezoelectric film 443 is mainly composed of a composite oxide containing potassium (K), sodium (Na), and niobium (Nb) and having a perovskite structure represented by the general formula ABO3. In detail, the above-mentioned composite oxide is represented by the following formula (5).

[0077] (K m Na1-m NbO3…(5)

[0078] Equation (5) satisfies 0.1≤m≤0.9.

[0079] The potassium sodium niobate composite oxide of formula (5) is a lead-free piezoelectric material with suppressed lead and other content, and it is called a KNN-type composite oxide. KNN-type composite oxides are beneficial for reducing environmental impact, and they are superior in piezoelectric properties compared with other lead-free piezoelectric materials. Furthermore, since KNN-type composite oxides have a higher Curie temperature than other lead-free piezoelectric materials such as BNT-BKT-BT, and are less prone to depolarization caused by temperature rise, they are more advantageous for use at high temperatures.

[0080] In formula (5), the potassium content is preferably set to 30 mol% or more and 70 mol% or less relative to the total amount of metal elements constituting the A-site of ABO3. That is, preferably, m satisfies 0.3 ≤ m ≤ 0.7. More preferably, the potassium content is set to 40 mol% or more and 60 mol% or less relative to the total amount of metal elements constituting the A-site. That is, more preferably, m satisfies 0.4 ≤ m ≤ 0.6. As a result, the piezoelectric properties of the piezoelectric film 443 can be improved.

[0081] In addition to the KNN-type composite oxide of formula (5), the piezoelectric film 443 also contains lithium and one or more first transition elements. Examples of first transition elements include scandium (Sc), titanium, vanadium (V), chromium (Cr), manganese (Mn), iron, cobalt (Co), nickel (Ni), copper (Cu), and zinc (Zn).

[0082] The aforementioned elements can be included as additives in the KNN-type composite oxide of formula (5). Specifically, the KNN-type composite oxide contained in the piezoelectric film 443 is not limited to the composition shown in formula (5), but may, for example, be the composition shown in formula (6) below.

[0083] {K n Na 1-n} q-o Li o}(Nb 1-p M p O3…(6)

[0084] Where M refers to the first transition element, and satisfies 0.1≤n≤0.9, 0.9≤q≤1.2, 0.03≤o≤0.05, p≤0.05.

[0085] By including lithium in the piezoelectric film 443, the diffusion of elements such as bismuth from the seed layer 442 into the piezoelectric film 443 is reduced during processes such as heat treatment in the manufacturing of the piezoelectric element 44. This improves the piezoelectric properties of the piezoelectric element 44. The lithium content in the piezoelectric film 443 is preferably set to 10 mol% or less.

[0086] Here, the piezoelectric film 443 is divided into two equal parts vertically along the stacking direction, i.e., along the Z-axis. The upper side of the second electrode 444 is designated as the first region 443f, and the lower side of the first electrode 441 is designated as the second region 443s. When the elemental concentration in the depth direction is measured from the top surface of the piezoelectric film 443 using secondary ion mass spectrometry (SIMS), the bismuth intensity measured by SIMS at the boundary between the first region 443f and the second region 443s is less than one-five-hundredth of the maximum bismuth intensity measured by SIMS in the piezoelectric film 443.

[0087] Bismuth diffuses from the seed layer 442 into the piezoelectric film 443. Therefore, the maximum bismuth intensity in the piezoelectric film 443 is measured at the surface of the piezoelectric film 443 on the seed layer 442 side. In other words, in the piezoelectric film 443, the bismuth concentration is higher at the surface in contact with the seed layer 442, and decreases upwards. By suppressing the bismuth intensity at the boundary between the first region 443f and the second region 443s to less than one-five-hundredth relative to the bismuth intensity at the surface of the piezoelectric film 443 in contact with the seed layer 442, it becomes difficult to generate high concentrations of defects in the crystallization of the piezoelectric film 443. Therefore, the piezoelectric characteristics of the piezoelectric element 44 can be improved.

[0088] Furthermore, by including one or more first transition elements in the piezoelectric film 443, the leakage current in the piezoelectric element 44 is reduced. This improves the electrical characteristics of the piezoelectric element 44.

[0089] The piezoelectric film 443 may also include a piezoelectric material as a mixed crystal, wherein the mixed crystal is a mixed crystal containing potassium, sodium, and niobium and having a perovskite structure represented by the general formula ABO3, and other mixed crystals having a perovskite structure represented by the general formula ABO3. Furthermore, the piezoelectric material included in the piezoelectric film 443 may also include materials having a composition lacking some of the aforementioned elements, materials having a composition with a partial excess, etc.

[0090] The piezoelectric film 443 is oriented towards the {100} orientation. That is, the piezoelectric film 443 is preferably oriented towards the (100) plane. This can further improve the piezoelectric characteristics of the piezoelectric element 44. Here, in this specification, preferred orientation means that 50% or more, and preferably 80% or more of the crystals are oriented towards a specified crystal plane. Specifically, preferred orientation towards the (100) plane means that all the crystals of the piezoelectric film 443 are oriented towards the (100) plane, and at least 50% or more of the crystals are oriented towards the (100) plane. The crystal orientation of the piezoelectric film 443 can be determined by analyzing the X-ray diffraction pattern of X-ray diffraction. The thickness of the piezoelectric film 443 is, for example, set to be 50 nm or more and 2000 nm or less.

[0091] A second electrode 444 is formed on the piezoelectric film 443. The second electrode 444 is disposed such that it covers the top and sides of the piezoelectric film 443, a portion of the side of the seed layer 442, and the top of the vibrating plate 36 in region 443a. The second electrode 444 is made of a platinum layer. The second electrode 444 is not limited to being made of a platinum layer; it may also be a single layer of a metal material such as iridium, aluminum, nickel, gold, or copper, or a structure consisting of two or more single layers of the aforementioned metal materials stacked together.

[0092] Although this embodiment illustrates a piezoelectric element 44 formed by sequentially stacking a first electrode 441, a seed layer 442, a piezoelectric film 443, and a second electrode 444 on a vibrating plate 36, it is not limited to this. The piezoelectric element of the present invention may, for example, be a vertically vibrating type piezoelectric element in which piezoelectric materials and electrode forming materials are alternately stacked and stretched in the axial direction.

[0093] 1.4. Manufacturing Method of Piezoelectric Elements

[0094] The following describes an example of a method for manufacturing the piezoelectric element 44. First, a vibrating plate 36 is fabricated. Specifically, a silicon substrate 361 is thermally oxidized to form silicon oxide on its surface. Next, after covering the silicon oxide with a zirconium layer by sputtering, the zirconium layer is thermally oxidized to form a zirconium oxide layer as an insulating layer 362.

[0095] Next, the first electrode 441 is formed. Specifically, a platinum layer and then an iridium layer are stacked densely on the surface above the insulating layer 362 by sputtering. Then, the platinum and iridium layers are patterned by photolithography. Specifically, a photoresist is coated onto the iridium layer and exposed, and ion milling is performed on the platinum and iridium layers. Next, the photoresist is removed by oxygen plasma ashing polishing, and cleaning is performed.

[0096] Next, a seed layer 442 is formed using the MOD (Metal Organic Decomposition) method. Specifically, a propionic acid solution of lead, bismuth, iron, and titanium is prepared as the precursor solution for the seed layer 442. The molar ratio of each element is set, for example, as lead:bismuth:iron:titanium = 10:110:50:50. The propionic acid solution is then spin-coated onto a vibrating plate 36 on which the first electrode 441 is formed. Next, after drying and degreasing at 350°C using a hot plate, a heat treatment is performed at 650°C for three minutes using RTA (Rapid Thermal Annealing) achieved by an infrared lamp or similar device. This forms a full-surface layer including the seed layer 442.

[0097] Next, a layer forming the piezoelectric film 443 is formed by a solution method. First, a precursor solution for the piezoelectric film 443 is prepared. The precursor solution contains, as a solute, metal complexes of potassium, sodium, niobium, lithium, and a first transition element. The solvent of the precursor solution is an organic solvent capable of dissolving or dispersing the metal complexes. In this embodiment, manganese is used as the first transition element.

[0098] Specifically, potassium isooctanoate, sodium isooctanoate, niobium isooctanoate, lithium isooctanoate, manganese isooctanoate, etc., are used as the aforementioned metal complexes. In the solvent, organic solvent monomers or mixtures such as ethylene glycol monobutyl ether or n-octane are used. The content of each metal complex in the precursor solution corresponds to the desired molar ratio of each element in the piezoelectric film 443.

[0099] The precursor solution is coated onto a layer including the seed layer 442 using a spin coating method. Next, after drying at 180°C using a hot plate and degreasing at 380°C, a heat treatment of 700°C for three minutes is performed using RTA. This promotes the crystallization of the composite oxide of the piezoelectric film 443. Furthermore, a full-surface layer including the piezoelectric film 443 is formed. In addition, to increase the thickness of the piezoelectric film 443, the process from coating the precursor solution to the RTA heat treatment can be repeated.

[0100] Next, the aforementioned region 443a is patterned. Specifically, in the layer including the seed layer 442 and the layer including the piezoelectric film 443, the region corresponding to region 443a is removed, thereby forming the seed layer 442 and the piezoelectric film 443. As a method for patterning, dry etching such as reactive ion etching or ion milling, or wet etching using an etchant, can be employed.

[0101] Next, a second electrode 444 is formed above the piezoelectric film 443 and region 443a. Specifically, similar to the first electrode 441, a platinum layer is deposited as the second electrode 444 by sputtering. As described above, the piezoelectric element 44 is manufactured.

[0102] The following effects can be obtained according to this embodiment.

[0103] By including lithium in the piezoelectric film 443, the diffusion of bismuth contained in the seed layer 442 into the piezoelectric film 443 is suppressed. In particular, the concentration of bismuth diffusing into the piezoelectric film 443 is maximized near the surface on the seed layer 442 side and decreases from the seed layer 442 side toward the second electrode 444 side. Therefore, by setting the bismuth intensity at the boundary between the first region 443f and the second region 443s to less than one-five-hundredth of the bismuth intensity on the surface on the seed layer 442 side, the concentration of bismuth in the piezoelectric film 443 is suppressed, thereby improving the piezoelectric characteristics of the piezoelectric element 44. Furthermore, by including one or more first transition elements such as manganese in the piezoelectric film 443, leakage current can be reduced. As described above, a piezoelectric element 44, a droplet ejector head 1, and an actuator 101 with improved electrical characteristics can be provided.

[0104] 2. Examples and Comparative Examples

[0105] The following examples and comparative examples are shown, and the effects of the above-described embodiments are explained in more detail.

[0106] 2.1. Manufacturing of piezoelectric elements

[0107] In the piezoelectric element 44 of Example 1, the molar ratio of each element contained in the piezoelectric film 443 was set as potassium:sodium:lithium:niobium:manganese = 0.5151:0.4949:0.0500:0.9950:0.0050. Furthermore, the process from coating the precursor solution to the heat treatment by RTA was repeated five times. Apart from these conditions, the piezoelectric element 44 was manufactured by performing the processing according to the manufacturing method described above.

[0108] In the piezoelectric element of Comparative Example 1, lithium was removed from the elements contained in the piezoelectric film 443 of Example 1, and the molar ratio of each element contained in the piezoelectric film was set to potassium:sodium:niobium:manganese = 0.54:0.52:0.995:0.005. Except for this condition, the piezoelectric element of Comparative Example 1 was manufactured in the same manner as the piezoelectric element 44 of Example 1.

[0109] In the piezoelectric element of Comparative Example 2, the seed layer 442 was omitted from the piezoelectric element 44 of Example 1, and the piezoelectric element of Comparative Example 2 was manufactured in the same manner.

[0110] 2.2 Evaluation of piezoelectric elements

[0111] 2.2.1. Crystalline Orientation of Piezoelectric Films

[0112] The crystal orientation of the piezoelectric film of the piezoelectric element in Example 1 and Comparative Examples 1 and 2 was investigated using X-ray diffraction intensity curves measured by X-ray diffraction (XRD). Furthermore, in this analysis, samples extracted at a time point prior to the formation of the piezoelectric film and the second electrode in the manufacturing method of the aforementioned piezoelectric element were used.

[0113] The X-ray diffraction apparatus used was a Bruker D8 DISCOVER with GADDS. Measurement conditions were as follows: tube voltage set to 50 kV, tube current set to 100 mA, detector distance set to 15 cm, collimator diameter set to 0.3 mm, and measurement time set to 120 seconds. The obtained two-dimensional data was converted into X-ray diffraction intensity curves using the apparatus's software, with the 2θ range set to 20°–50°, the χ range set to -95°–-85°, the step size set to 0.02°, and the intensity normalization set to Bin normalized.

[0114] The results showed that the peak intensity of the (100) plane was stronger in the X-ray diffraction intensity curves of Example 1 and Comparative Example 1, thus confirming the preferred orientation of the composite oxide of the piezoelectric film towards the (100) plane. In contrast, the peak intensity of the (100) plane was very weak in the X-ray diffraction intensity curve of Comparative Example 2, and the peaks of the (110) plane were mixed together. Therefore, it can be seen that the composite oxide of the piezoelectric film in Comparative Example 2 is randomly oriented. This demonstrates the effectiveness of the seed layer for the crystal orientation of the piezoelectric film.

[0115] 2.2.2. Diffusion of bismuth from the seed layer to the piezoelectric film

[0116] Compositional analysis was performed on the piezoelectric film of the piezoelectric element of Example 1 and Comparative Example 1 by SIMS from the surface of the second electrode side to the seed layer side in the -Z direction as the depth direction.

[0117] The SIMS device used was a CAMECA IMS-7f fan-shaped SIMS. Measurements were performed using 15 kV ions (Cs+) as primary ions, with a 10 nA beam current scanned at a 100 μm angle, and negative secondary ions detected from the center at a 33 μm φ. An electron gun was used during measurements to suppress charge rise.

[0118] exist Figure 6 as well as Figure 7 The obtained depth-direction curve is represented in the diagram. Additionally, for ease of illustration, in Example 1... Figure 6 In the example shown, only niobium, bismuth, iridium, and lithium are present, as in Comparative Example 1. Figure 7 Only niobium, bismuth, and iridium are shown. Figure 6 as well as Figure 7 In the diagram, the horizontal axis represents the time (in seconds) of excavation in the depth direction, which can also be considered as the distance in the -Z direction. The vertical axis represents the detection intensity of each element.

[0119] like Figure 6 As shown, in Example 1, the boundary s1 where niobium begins to be detected is the surface of the second electrode 444 side of the piezoelectric film 443, and the boundary s3 where the intensity of niobium rapidly decreases is the surface of the seed layer 442 side of the piezoelectric film 443. Therefore, when the piezoelectric film 443 is bisected in the stacking direction, i.e., along the Z-axis, with boundary s2 as the boundary, the second electrode 444 side becomes the first region 443f, and the first electrode 441 side becomes the second region 443s.

[0120] The maximum bismuth (Bi) intensity b in the piezoelectric film 443 was detected at boundary s3, which was approximately 47800 cps. The bismuth intensity gradually decreased from boundary s3 towards boundary s1, and the bismuth (Bi) intensity a at boundary s2 was approximately 88 cps. Table 1 shows the above-mentioned bismuth intensities a and b, as well as the value a / b obtained by dividing the bismuth intensity a by the maximum bismuth intensity b. In Example 1, a / b was 0.00184, which is 1 / 500, or less than 0.0020.

[0121] Table 1

[0122]

[0123] like Figure 7 As shown, in Comparative Example 1, the boundary s11 where niobium begins to be detected is the surface of the second electrode side of the piezoelectric film, and the boundary s13 where the intensity of niobium rapidly decreases is the surface of the seed layer side of the piezoelectric film. Therefore, when the piezoelectric film is bisected in the stacking direction, i.e., along the Z-axis, with boundary s2 as the boundary, the second electrode 444 side becomes the first region 443g, and the first electrode side becomes the second region 443t.

[0124] The maximum bismuth (Bi) intensity b in the piezoelectric film was detected at boundary s13, which was approximately 58600 cps. The bismuth intensity gradually decreased from boundary s13 towards boundary s11, with the bismuth (Bi) intensity a at boundary s1 being approximately 395 cps. Table 1 shows the bismuth intensities a and b, as well as the value a / b obtained by dividing the bismuth intensity a by the maximum bismuth intensity b. The a / b ratio for Comparative Example 1 was 0.00674, which exceeded 1 / 500, or 0.0020.

[0125] Based on the above, Example 1 demonstrates a situation where the diffusion of bismuth from the seed layer 442 to the piezoelectric film 443 is suppressed compared to Comparative Example 1. Therefore, it can be seen that the piezoelectric element 44 of Example 1 is more advantageous in terms of improved electrical characteristics compared to the piezoelectric element of Comparative Example 1.

[0126] 2.2.3. Diffusion of bismuth from the seed layer to the piezoelectric film

[0127] Hysteresis measurements of the applied electric field and polarization were performed on the piezoelectric elements of Example 1 and Comparative Example 1. Specifically, in Example 1, the probe was brought into contact with the first electrode 441 and the second electrode 444, respectively, with the first electrode 441 as the positive electrode, and the applied electric field was adjusted to 300 kV / cm at a frequency of 66 Hz to measure the historical curve. The results were then... Figure 8 The lines are represented by solid lines. In Comparative Example 1, the historical curves were measured using the same method as in Example 1, and the results were displayed... Figure 8 The middle part is represented by a dashed line.

[0128] like Figure 8 As shown, Example 1 exhibits a greater amount of saturated polarization and residual polarization compared to Comparative Example 1, resulting in superior ferroelectricity.

[0129] 3. Second Implementation Method

[0130] Although the droplet ejector 1 and the recording device 100 with the applicable piezoelectric element 44 have been illustrated in the above embodiments, the application of the piezoelectric element of the present invention is not limited thereto. The piezoelectric element of the present invention can be applied to ultrasonic sensors, piezoelectric motors, ultrasonic transformers, vibratory dust collectors, pressure-to-electric converters, ultrasonic transmitters, pressure sensors, and accelerometers, etc.

[0131] Specifically, the piezoelectric element of the present invention can also be applied to an oscillator. The oscillator of this embodiment includes the piezoelectric element 44 of the above-described embodiment, and has a charge detection unit that detects the amount of charge generated by the displacement of the piezoelectric element 44 and outputs a signal corresponding to the detected charge amount. Therefore, an oscillator with superior vibration characteristics and detection sensitivity can be provided because it can improve the piezoelectric characteristics of the piezoelectric element 44 and reduce electrical characteristics such as leakage current.

[0132] Furthermore, the piezoelectric element of the present invention can also be mounted on a power generation device. Examples of power generation devices include those utilizing pressure-electric conversion effects, those utilizing electron excitation achieved by light, those utilizing electron excitation achieved by heat, and those utilizing vibration.

[0133] Furthermore, the piezoelectric element of the present invention can also be applied to ferroelectric elements in thermoelectric devices such as infrared detectors, terahertz detectors, temperature sensors, and thermistors, or ferroelectric memory devices.

[0134] Symbol Explanation

[0135] 1…droplet ejector head; 34…pressure chamber substrate; 36…vibrating plate as substrate; 44…piezoelectric element; 50…drive circuit as voltage application part; 62…nozzle plate; 101…actuator; 441…first electrode; 442…seed layer; 443…piezoelectric film; 443f…first region; 443s…second region; 444…second electrode; C…pressure chamber; N…nozzle; s2…boundary; Ts…thickness of seed layer; Tu…thickness of first electrode.

Claims

1. A piezoelectric element comprising: The first electrode is formed on the substrate; A seed layer is formed on the first electrode; A piezoelectric film is formed on the seed layer and contains potassium, sodium and niobium; The second electrode is formed on the piezoelectric film. The piezoelectric film contains lithium and one or more first transition elements selected from scandium, titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, and zinc. The seed layer contains bismuth. When the piezoelectric film is divided into two equal parts in the stacking direction, and the second electrode side is designated as the first region and the first electrode side as the second region, the bismuth intensity at the boundary between the first region and the second region, as measured by secondary ion mass spectrometry, is less than one-five-hundredth of the maximum bismuth intensity of the piezoelectric film as measured by secondary ion mass spectrometry.

2. The piezoelectric element as claimed in claim 1, wherein, The seed layer contains titanium, iron, and lead.

3. The piezoelectric element as described in claim 2, wherein, In the stacking direction, the thickness of the seed layer is thinner compared to the thickness of the first electrode.

4. The piezoelectric element according to any one of claims 1 to 3, wherein, The piezoelectric film is preferentially oriented toward the (100) plane.

5. A droplet ejector head comprising the piezoelectric element and substrate as described in claim 1, and further comprising: A nozzle plate having nozzles that eject liquid droplets; A pressure chamber substrate, which forms a pressure chamber communicating with the nozzle. The substrate forms part of the wall of the pressure chamber. The piezoelectric element is formed on the substrate.

6. An actuator comprising the piezoelectric element of claim 1, and further comprising: A drive unit, which is driven by the piezoelectric element; The voltage application section applies a voltage to the piezoelectric element.

7. An oscillator comprising the piezoelectric element of claim 1, and further comprising: The charge detection unit detects the amount of charge generated by the displacement of the piezoelectric element and outputs a signal corresponding to the amount of charge.

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